Remote-control system



G. W.- BAUGHMAN mm comop SYSTEH Filed mi. 15, 1944 IN Y my M 2 a mi; m. 9 H W a \W Max:126, 194s.

. III-lull In b a fiw' Patented Mar. 26, 1946 REMOTE-CONTROL SYSTEM George W. Baughman, Swissvale, Pa., assignor to The Union Switch & Signal Company, Swissvale, Pa.,'a corporation of Pennsylvania Application November 15, 1944, Serial No. 563,608

Claims.

My invention relates to remote control systems and more particularly to the line circuits for such systems of the normally closed bridged type such as shown, for example in the United States Patent No. 2,303,875, issued December 1, 1942, and No. 2,350,668, issued June 6, 1944, to G. W. Baug man and N. F. Agnew for remote control systems.

In systems of this character a line circuit is employed which extends from the control office through a plurality of field stations at spaced locations within the controlled territory, by means of which a line relay at each station connected across the line is normally energized by line current from a central battery located at the office. Control codes are transmitted from the office at times to which coding units controlled by the station line relays are selectively responsive by periodically interrupting at the oilice the supply of line current from the ofiice line battery. The station coding units are also adapted to transmit indication codes to the office at times over the same line wires by periodically connecting the line wires together at the transmitting station through a low impedance to vary the current delivered. to the line circuit by the oflice battery, the indication codes being received by a line relay at the office of the stick polar type which is connected to the line through a transformer.

Since the station coding units are capable of initiating codes at any time the line is free, one requirement for systems of this character is the provision of means for preventing interference so as to give only one station access to the line at a time. This is accomplished by the use of line relays at the stations which are responsive to current of one polarity, and by the provision of means controlled by the office line relay in response to the first impulse of a received code for reversing the line polarity and at the same time reversing the connections of the line relay at the transmitting station, so that during the transmission of the code onlythe line relays at the ofiice and at the transmitting station respond to the code, the others remaining released until the line polarity is restored to normal at the end of the code. To prevent interference between the transmitters at tWo or more stations which initiate codes at the same time, a current limiting resistance is interposed between the line battery and the line to render the connection between line wires due to the operation of the transmitter at a station near the ofiice, eflective to shunt the line to control the line relay at any more remote station so as to cause the latter to respond to a code which differs from the one which the associated coding unit is capable of transmitting; a lock out circuit in the station coding unit serving to discontinue the operation of the transmitter at the more remote stations under this condition.

The object of the present invention is to improve the efficiency of transmission in systems of the type described so as to adapt them to operation over line circuits which are relatively long, electrically, or which have line wires of relatively high resistance.

I shall describe one form of apparatus embodying my invention and shall then describe the novel features thereof in claims.

Referring to the accompanying drawing Fig. 1 shows a typical line circuit for a remote control system of the type described,'modified in accordance with my invention comprising a pair of line wires Y and Z extending from the control office, shown at the left, through a plurality of similarly arranged field stations of which one is shown in the right hand portion of the drawing over which the line relays R at each station are normally energized in multiple by current from a line battery 80 located at the ofiice. Fig. 2 shows a modification of that portion of the apparatus of Fig. 1 which is located atthe control ofiice for regulating the voltage supplied by the line battery in accordance with a feature of my invention.

Similar reference characters refer to similar parts in each of the views.

Referring to Fig. 1, the line circuit may be traced from battery 80 through the primary windings of an impulse transformer 4, the secondary of which is connected to the oflice line relay OR to render relay OR responsive to variations in' line current, thence over back contacts I) and d of an ofiice transmitter relay OT and of a pole changer relay 'PC through the coils of a low pass filter I2 to the line wires Y and Z the filter 52 being included in the circuit to enable the line wires to be used jointly for telephone communication or other purposes. At each station a conv nection across the line wires Y and-Z is normally is not to polarize the relay, but rather to block the flow of current through the relay when its polarity is such that the relay is incapable of responding thereto.

The office line relay OR is of the magnetic stick type arranged to be held in its last operated position when deenergized and is controlled locally as described in the above mentioned patents so that it is automatically restored to its normal position after a time interval if it is accidentally reversed and in that manner is maintained in its normal position as shown, when the system is at rest.

Except for the added rectifier 6, the station apparatus is generally similar to that of Patent No. 2,303,875. The office apparatus is also gen. erally similar to that of this patent, except for the addition of a biasing circuit for relay OR controlled by contact of relay PC as shown. These modifications donot change the normal mode of operation of the system which will now be briefly described.

Each line relay OR or R controls a coding unit CU which is normally conditioned to receive codes and which may be caused to transmit codes at times the transmitting condition being manitested by the energization of a master relay OM or M. When the ofiice master relay OM is energizedto initiate. the transmission of a control code to the stations, itcompletes a circuit at its contact e governed by the ofiice coding unit for periodically energizing the transmitter relay 0T, contacts b and d which periodically interrupt the line current of normal polarity to operate the line relays R at the several stations to control the station coding units in accordance with the code, while contact e of relay OT completes circuits over front contact h of relay OM for supplying current of reversible polarity locally to the lower winding of relay OR to. cause the ofiice codin unitto respond to the code, the upper or line winding of relay OR being temporarily disconnected from transformer 4 by the operation of contact 0 of relay OM.

When the master relay M at a field station is V energized to initiate the transmission of an indication code to the oflice, the operation of its pole changer contacts a and k reverses the connections of the associated line relay R, and at the" same time completes a connection from line Y over its front contact 70 and the back contacts :2

and b of the relays LBP and E of the station coding unit to line Z causing relay R at the transmitting station to release While increasing the current delivered by the line battery 80 through transformer 4 to induce an impulse therein to reverse relay OR. Relay PC now picks up over the circuit from terminal B of the local onice battery over contacts b of relays OLBP and OM through relay PC to terminal C and relay OLBP is energized by the ofiice coding unit to complete a stick circuit at its contact a to hold relay PC enerized until the'code is fully received as mani tested by the operation of a relay O16 controlled by the ofiice coding unit. The operation of contacts b and d of relay PC reverses the polarity of the current supplied to the line thereby releasing relay R at each station other than the transmitting station, that is, at each station at which relay M occupies its released position.

When the master relay at the transmitting station is energized it also completes a circuit at its contact e governed by the associated coding unit for periodically energizing the transmitter relay T. Relay LBP is energized by the coding unit in response to the first operation of relay its entirety when the line is again free in a well R, and then contact I) of relay T operates periodically to connect the line Wires together and to open the circuit for relay R. Since line wire Z is now positive, relay R picks up each time relay T releases during the transmission of the code over the connection from line wire Z over front contact a of relay M through relay R and over back contact I) of relay T and frontcontact k of relay M to line Wire Y and when relay T picks up the line wires are connected together through the coils l2 over front contacts is and b of relays M and T, and back contact b of relay E, consequently relay OR at the ofiice responds to the line current variations to control theofiice coding unit in accordance with the code and relay R at the transmitting station operates in unison therewith to control the coding unit by which re lay T is governed, while relays R- at the other stations remain released until the line polarity is restored to normal by relay PC at'the end of the code. e

In the event two stations initiate codes at the same time, the two relays T will operate in unison as long as the corresponding code steps are alike but the codes transmitted from the different stations differ in the length of one or more steps and a point is reached where relay T at one station either releases to generate'a short even numbered step while relay T at another station remains picked up to generate a corresponding long j step or the relay T at one station remains released 40 theconnection between wires Y and Z produced by relay T includes only the relatively low resistance of the coils l2 and is fully effective to release the line relays at more remote stations, but it is not necessarily eilective to release those at stations nearer the office because of the effect of the resistance of the intervening line wire. It will be seen therefpre that the line relays at the more. remote stations which are in the transmitting condition will be operated in accordance with the code transmitted by relay T at the station nearer the ofiice, and at such stations on one step or another relays R and T will both-be released for a time suificient to complete a lock out circuit which extends from terminal B at the right hand contact of relay R overback contact d of relay I, front contacts a and f of relays M and LBP through relay E to terminal C, whereupon relay E will become energized and open its back contact d to release relay M to stop further transmission from the-more remote station, the interrupted code being stored for transmission in known manner.

Considering now the modifications of the line circuit comprising'my invention, itwill be seen that if the system is applied to line circuits which are unusually long or of higher resistancernot only Willa higher line voltage be required for the proper operation of the more remote line relay but the percentage change in line current due to the operation of their transmitter relays will be smaller due to the increased resistance of the intervening line .wires and to the. increased current flow through the line relays nearer the oflice. When the rectifier 6 is interposed in the circuit for each line relay R, as shown, the transmitting relays T at the more remote station are rendered capable of causing much larger variations in-line current so that the operation of the oflice line relay OR is more positive for the. reason that the flow of current through the line relays R at the other stations which are not inthe transmitting condition is blocked by the rectifiers 6, decreasing the line current and increasing the voltage across line wires Y and Z at the remote transmitting tation, and the system is thereby adapted for use over line circuits which are electrically longer or of unusually high resistance.

It will be seen that this expedient is ineffective under two conditions: (1) When a number of stations initiate codes at the'same time; but in this case the operation of the transmitters at the more remote stations is not required, a already explained. (2) When the system is in its normal at rest condition with current of normal polarity supplied to the line. In the latter case, in order to initiate the transmission of a code by the operation of the transmitter relay at the most distant station, it is necessary to have the office line relay OR normally in condition to respond to an increase in line current of a materially smaller value than that by which it is operated in response to the successive steps of the code. This is accomplished by biasing relay OR so as to overcome in part the magnetic-force by which it is held in its normal position by the provision of a local circuit for relay OR which includes back contact of relay PC and back contact h of relay OM, as shown, which circuit is closed only when the system is inits normal at rest condition. I

It will be seen therefore that while relay OR is normally in condition to respond to an impulse tending to operate it to reverse which is so weak that the relay would not respond properly to a succession of such impulses constituting a code, the operation of relay PC by the initial operation of relay OR reverses the line polarity and renders the rectifiers 6 effective to suppress the flow of current through the line relays at other stations so that the code impulses supplied to relay OR. are relatively strong and its reliable operation is thereby insured.

In a long line circuit arranged a described it I will be evident that a relatively high voltage line battery may be required and that since the drop through the current limiting resistances and the oflice filter coils is decreased, due to the decrease in the line current, When a station is transmitting, the changes in the line current due to the operation of a transmitter at a station near the oflice may be unduly large overloading the filter coils so as to produce noise in a telephon circuit superimposed upon the line wires Y and Z.

This difficulty is overcome by the provision or the arrangement illustrated in Fig. 2, comprising an additional line relay ORA connected to the line through an impulse transformer 4A in series with the transformer 4 by which the relay OR controlling the office coding unit is controlled. Relay ORA is controlled like relay OR but responds only to a relatively large change in line current as produced by the initial operation of a transmitter at a nearby station, due. to the provision of an adtustableresistance. 1 for shuntingits line winding to render the relay less sensitive. The high voltage line battery is divided into two sections a and 810i) and when relay ORA reverses it completes a pick-up circuit for a stick relay PC I, which relay becomes energized in response to the reversal of relay ORA and by removing section 8027 of the line battery from the circuit reduces the line voltage to the desired value. Relay OR which reverses at the sametime, energizes: relay PC as already described in connection with Fig. 1 and relay PC completes a stick circuit for holding relay PC'l energized until the end of the code.

It is tov be. understood that the system includes means for preventing the response of relay OR to the current variations caused by the reversal of polarity of the line current by relay PC. Relay-PC controls a slow acting repeater relay PCP as shown in Fig. 2 and circuits jointly controlled by relays PC and PCP serve to open the connection between relay OR and transformer t when relay PC picks upor releases and to complete local. circuits to hold relay OR reversed for a brief period when relay PC picks up and to hold relayOR normal for a corresponding period when relay PC releases. These circuits are also effective to prevent the'response of relay OR tothe changes in line current due to the pick up or release of relay PCI, as Will be readily apparent.

Due to the marginal adjustment of relay ORA provided by resistance 1 if this relay were connected permanently in circuit it might fail to operate on the initial impulse of a code from an intermediate station and might operate in response to one of the succeeding impulses of that code and thereby interfere with its proper reception. For this reason relay ORA is disconnected from transformer 4A during the transmission of control codes by including a back contact of the master relay M in its circuit, as shown. and is also disconnected from transformer 4A when relay PCI picks up. Relay PCP is picked up by relay PC during the reception of the initial impulse of an indication code and completes a loo a1 circuit as shown, for restoring relay ORA to normal. This local circuit is effective to hold relay ORA normal and non responsive to the increase in line current due to the release of relay PCI at the end of the code, and also to hold relay ORA normal during the reception of a code. even though relay PCI is not operated. It will be seen therefore that relay ORA provides means effective when the line current variations transmittedfrom the more remote stations are increased for limiting the line current variations transmitted from nearby stations.

Although I have herein shown and described only one form of apparatus embodying my invention, it is to be understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, What I claim is:

1. In a remote control system, an ofiice and a plurality of stations connected by two line wires, a line relayof the biased polar type responsive to current of one polarity only having an electronic rectifier in series therewith passing current of only the one polarity to which such relay is responsive connected across the line wires at each station, a, source of current at the office normally supplying current of said'one polarity to the line wires to maintain all'sai'd'line relayszenergized a line relay at the ofl'ice responsive to variations in the current supplied to said, line circuit, a master relay at each station effective when energized to reverse the connections of the associated line relay and rectifier to render such relay responsive only to line current of reverse polarity and to momentarily connect the line wires totogether to operate the oflice line relay in accordance with a code, means comprising the electronic rectifiers at the other stations for blocking the flow of current through the line relays at such stations to increase the efiect of the operation of said transmitter relay, and means at the ofiice for biasing the ofiice line relay to render it responsive to a smaller variation in line current when the polarity is normal than when it is reversed. a l

.2. In a remote control system, an ofiice and a plurality of stations connected by two line'wires, a line relay having an electronicrectifier in series therewith passing current of one polarity only connected across the line wires at each station, a source of current at the office normally supplying current of said one polarity only to the line wires to maintain all said line relays energized, a master relay at each station adapted 'to become energized only when the associated line relay is ener gized to establish momentarily a low resistance connection between the line wires ,andat th'e sametime to reverse the connections of the associated line relay to effect its release, a line relay at the oilice responsive to current variations in said line current, a pole changer relay controlled by the office line relay for reversing the polarity of the current supplied to the line circuit when the master relay at any station becomes energized to thereby interrupt the supply of current to the line relays at other stations at which the master relays are not energized, a transmitter relay at each station'rendered effective when the associated line relay is energized to periodically vary the current supplied to the associated line relay to control the office line relay in accordance with a code and means efiective when said linecurrent is of said one polarity and the line relays at all stations are energized for biasing the ofllce line relay when all said line relays are supplied with current to render said relay responsive to a smaller variation in line current than is available for the operation of the relay when only one line relay is supplied with current.

3. In a remote control system, an ofilce and a plurality of stations connected by two line wires, a line relay having an electronic rectifier in series therewith passing current of one polarity only connected across the line wires at each station, a

source of current 'at the oflice normally supplying current of said one polarity only to the line wires to maintain all said line relays energized, a line relay at the ofiice inductively coupled to the line circuit and responsive to predetermined variations in the line current, a pole changer at the ofilce for at times reversin the polarity of the line current to discontinue the supply of current to said line relays, means at each station for at times connecting the line wirestogeth'er to vary the line current, and means at the oflice for biasing said office line relay to render it responsive to a smaller variation in the line current when the polarity is normal than when it is reversed.

4. In a remote control system, an office and a plurality of stations connected by two line wires, a source of current of reversible polarity at the ofiice normally supplying current of one polarity to the line wires, a line relay at each station connected across the line wires having anrelectronic rectifier in series therewith passing current of said one polarity only, a pole changer relay at the ofiice for at times reversing the polarity of the current supplied to the line circuit, a line'relay at the ofiice responsive to variations in the current supplied to the line circuit for controlling said pole changer, code transmitting'means at each station for at times connecting the line wires together through a relatively low resistance to periodically increase the line current in accordance with a code to whichthe ofiice line relay is responsive and at the same time reversing the connections of the associated station line relay to render such relay responsive thereto, a second line relay at the oflice responsive only to the larger increases in the line current due to theropera; tion of the transmitters at nearby stations, and means controlled by said second line relay for supplying current of a reduced voltage to the line circuit from said source during the operation of such transmitters at nearby stations.

5. In a remote control system, an office and a plurality of stations connected by two line wires, a sourcetof current of reversible polarity at the ofiice normally supplying current of one polarity to the line wires, 3, line relay at each station connected across the line wires having an electronic rectifier in series therewith passing current of said one polarity only, a pole changer relay at the ofiice for at timesreversing the polarity of the current supplied to the line circuita line 'relay' at the ofiice responsive to variationsin the current supplied to the line circuit for controlling said pole changer, code transmitting. means at each station for at times connecting the line wires together through arelatively low'resistance to periodically increase the line current in accord-.

ance with a code to which the oflice line relay is responsive and at the same time reversing the connections of the associated station line relay to render such relay responsive thereto, a second line relay, at the office responsive only to the larger increases in the line current due to the operation of the transmitters at nearby stations, means effective when said second line relay fails to respond to the increase of line current by which a code is initiated for preventing its response to succeeding increases in line current during the transmission'of such code, and means controlled by said line relay when it responds to the initiation of a code for supplying current of a reduced voltage to the line circuit from said source until such code is completed. 1

GEORGE W. BAUGHMAN. 

